Thermionic tube



June 2, 1936. H. J. ROUND THERMIONIC TUBES Filed Sept. 14, 1923 INVENTOR H JOSEPH ROUND BY I ag Mme ATT NEY Patented June 2, 1936 UNITED STATES PATENT OFFICE THERMIONIC TUBE of Delaware Application September 14, 1928, Serial No. 305,882 In Great Britain October 1, 1927 1 Claim.

This invention relates to thermionic tubes or valves, and has for its principal object to provide an improved thermionic valve capable of delivering a large power output with comparatively low anode potential.

According to this invention a thermionic valve comprises a cathode, a control electrode, and an output electrode, the two last mentioned electrodes being positioned at substantially the same distance from the cathode.

Preferably the separation between control grid and output electrode is not greater than that between either and the cathode.

In a tube of the construction above referred to the effect of a positive potential applied to the output electrode on the electron stream from the cathode is completely neutralized by an equal negative potential applied to the control grid, hence the cutoff bias for the tube is a negative potential on the control grid equal to the positive potential on the output electrode. The working bias for the control grid is a negative potential at some point between the cutofi bias and zero.

The invention is illustrated in the accompanying drawing, in which Fig. 1 represents in elevation a tube according to the invention; and,

Fig. 2 represents a modification.

Referring to Fig. 1, a thermionic valve comprises a cathode I consisting of a hot filament in the usual Way, and encompassed by a control electrode 2 consisting of a helix of wire wound upon an imaginary cylinder of which the filament is the axis. The filament I is also encompassed by a second helix of wire 3, similar to the control grid and wound upon the same imaginary cylinder. This second helix, which is wound with its turns between the turns of the control electrode and is insulated therefrom and separated therefrom by a distance not exceeding the filamentcontrol electrode separation, acts as an output electrode.

In the modification illustrated in Fig. 2, an additional plate like electrode 4, formed as a cylindrical plate concentric with the control and output electrodes, is provided and is electrically connected to the said output electrode. 5

It will be seen that this plate-like electrode will, in effect, take most of the current and will therefore prevent the output electrode from carrying all the anode current.

In operation a suitable negative potential bias is applied to the control electrode to which is also applied the input potentials, and a low positiv'e potential is applied to the output electrode which functions as an anode.

Various modifications may be made in the mechanical constructions employed. For example, the control and output electrodes may be oval or flattened oval instead of circular in cross section, and may be formed of wire strip, stampings, or of strip placed radially.

It has been found that with valves -in accordance with the present invention, a high conductivity may be obtained with a voltage amplification factor of unity or approximating thereto, so that the said valves are very suitable for dealing with large power output at low voltages.

Having now particularly described my invention, what I claim is: p

In an electron discharge device the combination of an electron emitting cathode, two co-axial helical electrodes of the same diameter and pitch mounted with the turns of each helix between the turns of the other helix and with said cathode at the common axis of said helices, the arrangement being such that the distance between adjacent turns of the helical electrodes is substantially equal to the distance between the cathode and said turns, and a cylindrical plate electrode surrounding said helices and electrically connected to one of said helices.

HENRY JOSEPH ROUND. 

